1. Field of the Invention
The present invention relates to a separable bottom end stop for a slide fastener comprising a box, a box pin and an insert pin, which are provided at ends of a pair of fastener stringers.
2. Description of the Related Art
There are various configurations of separable bottom end stops for a slide fastener, each separable bottom end stop being molded integrally with ends of fastener stringers using thermoplastic synthetic resin. However, a common feature in structures of the separable bottom end stops is that the box pin and the insert pin are integrally molded with one end of opposing edges of the pair of fastener stringers at least so as to be fixed thereto. In addition, usually the box is molded in a shape of a thin rectangular box, and a cross-section taken parallel to a short arm direction of the box, the short arm having a partition wall in a center of an inner side thereof, presents substantially a shape of the letter xe2x80x9cHxe2x80x9d turned sideways. Further, side portions of a long-arm side of the box have slit-shaped openings respectively.
Right and left spaces of the box which are defined by the partition wall, include a box pin insertion hole and an insert pin insertion hole into which the box pin and the insert pin are inserted respectively from one end of the box. Because, as mentioned above, the box pin and the insert pin are respectively fixed to the opposing edges of the pair of fastener stringers, the fastener tape portion of the each fastener stringer is also inserted into the slit-shaped opening when the box pin or the insert pin is inserted into the respective insertion hole of the box.
In recent years, as disclosed in Japanese Patent Application Laid-Open Nos. 8-98707, 10-14617 and 2000-106917, protruding guide portions which extend substantially parallel with respect to the insert pin and the box pin are molded integrally with the inner face of the fastener tape side of the insert pin and the box pin, via thin guide portions. The thin guide portions and the protruding guide portions allow the insertion operation of the insert pin and the box pin into the respective insertion holes in the box to be carried out easily. In addition, with ensuring secure and smooth insertion of the insert pin and the box pin, the thin guide portions and the protruding guide portions have a function for stabilizing the separable bottom end stop and the attaching portion for said bottom end stop.
It is to be noted that in order to ensure flexibility of the thin guide portions between the protruding guide portions, and the box pin and the insert pin, nylon which is very flexible, is often used as a material for forming the separable bottom end stop. However, increased demand for matching with diversification of fashion in recent years and various colors spreads even to a field of slide fasteners and other types of fasteners. In addition, a rapid action to the demand has been required.
However, conventionally, nylon is not used so much as the material for forming the slide fastener except for the separable bottom end stop, and there is a limit to the amount used. Additionally, it is difficult for nylon to meet the demand for matching with various colors, and further, nylon has high hygroscopic property, so managing the material is difficult.
This invention was developed with the foregoing present situation in view, and a specific object of the invention is to provide a separable bottom end stop for a slide fastener having an excellent durability with a material used for various purposes in the relevant field and being colored easily.
Firstly, the inventors set out to select a material that would replace nylon as a thermoplastic synthetic resin material of the separable bottom end stop for a slide fastener. As disclosed in the publications listed above, polyacetal resins are used much in slide fasteners as well as in other types of fasteners. Polyacetal resin is hard and easily handled, and is easy to manage because it has low water absorptivity and the quality of it does not alter with time. In addition, molding can be carried out easily and various colors can be realized when using polyacetal resin.
However, the polyacetal resin is hard and stiff, but it is also brittle. As a result, the box pin, the insert pin and the protruding guide portions individually tend to break easily and further, adhesive strength with other material is low and stripping tends to occur easily. Generally, before the separable bottom end stop is molded integrally with a fastener tape, a reinforcing film or a tape made from other flexible material is adhered to a region of the fastener tape where the separable bottom end stop is molded. Therefore, in the case where polyacetal resin is used to form the separable bottom end stop, the separable bottom end stop itself can be stripped from the fastener tape easily.
To solve the problem of easy stripping, if a large number of holes are formed in the region of the fastener tape where the separable bottom end stop is molded, the resin of the material passes through the holes and connects front and rear surfaces of the fastener tape upon molding. As a result, jointing strength is increased so that stripping can be prevented. At the same time, breakage of the box pin and the insert pin can be avoided. However, especially when the box pin is inserted into the insert hole in the box and fixed thereto, or when the insert pin is inserted into the insert hole in the box or removed therefrom, the box pin or the insert pin is often bent with respect to the box around the thin guide portion between the protruding guide portion and the box pin or the insert pin. If degree of the bending is large, the thin guide portion will break easily. If the thin guide portion break, the configuration of the separable bottom end stop cannot be kept stable and the separating operation also becomes difficult.
According to the invention, the past problems are solved and at the same time, inconveniences resulting from use of polyacetal resin material are eliminated. The basic structure of the invention is a separable bottom end stop for a slide fastener comprising a box, a box pin, and an insert pin, in which protruding guide portions which protrude onto respective fastener tapes are integrally molded with side faces at the tape-side of the box pin and the insert pin, via thin guide portions, wherein the separable bottom end stop is formed of a polyacetal resin, and a distance d between each of outer side faces of the box and each of the protruding guide portions when the box pin and the insert pin are mounted into the box, and a protrusion height h of each of the protruding guide portions from a surface of each of the thin guide portions satisfy the following equation (I):
tanxe2x88x921(d/h)xe2x89xa733xc2x0xe2x80x83xe2x80x83(I) 
where dxe2x89xa00.
If the value of tanxe2x88x921 (d/h) is less than 33xc2x0, there will be a large degree of bending around the thin guide portion between the protruding guide portion and the box pin or the insert pin, and thus the thin guide portion will break easily. If the value of tanxe2x88x921 (d/h) exceeds 33xc2x0, the protruding guide portion will abut the side face of the box and there will be no further bending thus preventing breakage. Meanwhile, it is to be noted that, assuming that the distance d between each of the outer side surfaces of the box and each of the protruding guide portions is 0, that is, assuming that width dimension of the thin guide portion is made 0, it becomes difficult to insert the box pin and the insert pin into the insertion holes of the box and thus difficulty of the operation is increased. It is to be noted that in a conventional type separable bottom end stop made of nylon, the value of tanxe2x88x921 (d/h) is 12xc2x0 and the value is extremely small.